CACAO is a research Java Virtual Machine developed at TU Wien. It compiles the class binaries while running (no interpreter), resulting in faster execution. It is an academic project, originally developed by students doing practical training or diploma theses on specific topics.

The first version of CACAO was released at 1997 as a faster replacement for Sun's implementation of the Java Virtual Machine, which at that time only had an interpreter. Current Sun virtual machines also use just-in-time compiling.